1. Cellular Wireless Networks
Cellular wireless is an increasingly popular means of personal communication in the modern world. People are using cellular wireless networks for the exchange of voice and data over such devices as cellular telephones, personal digital assistants (PDAs), cellular modems, and other wireless communication devices (WCDs).
In a typical cellular wireless communication system, an area is divided into cells and cell sectors, each defined by a radiation pattern (on a particular frequency) from a respective base station or “base transceiver station.” Each base station is then typically connected with core network equipment that functions to provide connectivity with a transport network such as the public switched telephone network (PSTN) or the Internet for instance, and that may function to control base station operation and handoff of served client devices from one base station to another. Conveniently with this arrangement, a cellular phone or other WCD that is positioned within the coverage area of a given sector can communicate over an air interface with the base station and in turn via the core network equipment with entities on the transport network.
WCDs and base stations generally communicate with each other over a radio frequency (RF) air interface according to a defined air interface protocol, examples of which include CDMA, iDEN, WiMAX, TDMA, AMPS, GSM, GPRS, UMTS, EDGE, LTE, WI-FI, BLUETOOTH, and others now known or later developed. Such air interface communication typically occurs on a frequency known as a “carrier” (which may actually be a pair of frequencies, one for communications from the base station to the WCD, and another for communication from the WCD to the base station). On such a carrier, the base station may emit a pilot signal, which is a control signal that a WCD may detect as an indication of base station coverage. In particular, as the WCD moves into the coverage of a base station and is operating on the base station's carrier, the WCD may detect the base station's pilot signal. In response, the WCD may then hand off to operate in the indicated coverage area.
A wireless service provider typically operates numerous base stations in a given geographic region, to provide robust air interface coverage as WCDs move from one location to another. These cellular base stations are usually not associated with any subscriber or small group of subscribers in particular; rather, they are usually placed in publicly-accessible locations designed so that their coverage blankets cities, rural areas, etc. to be used by the service provider's customers generally. As such, these types of base stations are generally known as “macro base stations,” and the network that they collectively form, or to which they belong, is generally known as a “macro network.”
2. Femtocells
To address gaps in macro-network coverage (e.g., poor in-building coverage) and for other reasons, macro-network providers may offer their subscribers private base station devices known as “femtocells,” (also sometimes referred to as access point base stations, picocells, ubicells, microcells, or femto-, pico-, ubi-, or micro-base stations or base transceiver stations), which are essentially small, low-power, low-capacity, and low-cost versions of a macro base station. Femtocells may be approximately the size of a desktop phone or WiFi access point. As a general matter, if a user, in addition to having cellular wireless service (which may include data service) for their WCDs, also has high-speed (“broadband”) Internet access through another communication channel, a femtocell may communicate with the user's broadband router and may establish a virtual private network (VPN) connection via the Internet with the wireless service provider's core network (e.g., with a femtocell controller on the wireless service provider's network).
The femtocell may include a wireless communication interface that is compatible with the user's WCDs and that is arranged to serve the WCD in much the same way that a macro base station does, providing a pilot signal and so forth. With a femtocell positioned in a location where macro network coverage may be poor or unavailable, the user's WCD can thus be served by the femtocell in much the same way that the WCD would be served by a macro base station when within coverage of the macro network.
To avoid interference with macro network communication, a femtocell may operate on a different carrier than that used by macro base stations. Further, to facilitate handoff of WCDs from the macro network to a femtocell, the femtocell may emit a pilot “beacon” on the carrier frequency of the nearby macro network. The pilot beacon may include administrative messages and parameters that WCDs can use to connect with the femtocell and may thus serve to inform a WCD that the WCD may begin scanning for coverage on the carrier of the femtocell. Thus, when a WCD is operating in the macro network and approaches the coverage of a femtocell, the WCD may detect the femtocell's pilot beacon and responsively begin scanning the femtocell's carrier in search of a pilot signal to facilitate handoff to the femtocell.
A typical femtocell also includes a Global Positioning System (GPS) receiver for use in receiving and decoding GPS satellite signals. GPS signals may be used in a well known manner to determine the location of the femtocell, and the GPS-determined location of the femtocell may be used as a basis to authorize operation of the femtocell. In particular, upon startup, the femtocell may report its location via the broadband connection to the wireless service provider's core network, and an entity on the wireless service provider's network may determine whether the femtocell is allowed to operate at that location. If so, the entity may allow the femtocell to operate. Or if not, the entity may block operation of the femtocell.